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Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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750 FXUS65 KPSR 151014 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 314 AM MST Mon Jul 15 2024 .SYNOPSIS... Monsoonal moisture in place will continue to result in daily thunderstorm activity for the next several days. Activity through the first half of the week will be confined mainly to the AZ high terrain, with chances for the lower deserts increasing once again by the latter half of the week and through next weekend. Temperatures throughout the week will remain above normal with widespread moderate HeatRisk in place. && .DISCUSSION... A very active evening was observed across the south-central AZ lower deserts yesterday, including the greater Phoenix metro area, as a couple of colliding outflow boundaries were enough to overcome the convective inhibition in place and spark strong thunderstorm activity. Areas of dense blowing dust, strong to locally damaging winds, and locally heavy rainfall leading to areas of minor flooding were all observed. Activity as of midnight has quieted down across most of the region. Current objective analysis shows the monsoon high situated over the Four Corners area with southeasterly flow in place. Thus, moisture levels for today will not change that much from yesterday. However, given the very active evening that was observed yesterday, the atmosphere has been overturned and thus a much quieter day is more likely today across the south-central AZ lower deserts. This is reflected in the 00Z HREF guidance, which virtually shows very minimal activity for later today. Convection is still expected to fire up later this afternoon along the Rim as well as across portions of southeast AZ, which could send multiple outflows into the lower deserts later this evening with a 10-30% chance of gusty winds in excess of 35 mph. However, given the greater stability that will be in place from the convective overturning from yesterday`s activity, these outflows are not expected to be sufficient to generate additional storm activity across the lower deserts. Elsewhere, upslope flow is likely to generate a few storms across northwestern portions of Joshua Tree National Park as well as along the San Diego Mountains and the northern Baja chain this afternoon. Activity that develops along the San Diego Mountains and northern Baja chain could drift into western portions of Imperial County. Heading through the middle of the week, the monsoon high is expected to shift slightly southward towards the Arizona/New Mexico border. This slight southward shift will lead to increased subsidence aloft, leading to slightly drier air and lesser instability. Moisture will still be more than enough to continue to fire up afternoon/early evening convection across the AZ high terrain, but given the increased subsidence and lesser instability in place, very minimal activity is expected across the lower deserts with outflow winds from the higher terrain activity still capable of resulting some gusty winds. Heading towards the latter half of the week and especially next weekend, the center of the high is expected to reposition north-northwestward towards southern Nevada with moisture increasing once again as global ensembles show PWATs rising to above 1.5" across the region. Thus, a more active monsoon pattern is likely to setup. With the high center repositioning over southern Nevada, the steering flow will switch out of the northeast, which will be a favorable trajectory for thunderstorms that develop over the Rim to migrate into the south- central AZ lower deserts. Temperatures this upcoming week will remain above normal but below excessive heat thresholds with widespread moderate HeatRisk in place. High temperatures across the lower deserts today and Tuesday will range between 107-111 degrees and then rise slightly to between the 110-114 degree range during the middle and latter half of the week as high pressure slightly strengthens over the region. Even though extreme heat is unlikely, it will still be hot enough that the necessary heat precautions should still be taken if engaging in outdoor activities. && .AVIATION...Updated at 0045Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: VCTS/TSRA conditions are expected to continue over the next couple of hours, mainly at KPHX and KIWA. Outflow winds will continue result in low confidence directions and speeds going into the overnight hours, but a S-SW component is favored for at least KPHX and KIWA. Less certainty if a southerly outflow could potentially reach KSDL and KDVT, so a northerly component wind is favored going into the overnight hours. Otherwise, winds are expected to remain westerly or become variable during the overnight hours prior to early westerly component winds developing at all terminals tomorrow morning. Occasional afternoon gusts 20-25 kts will be possible. Thunderstorm activity is anticipated to remain in the higher terrain, so the main uncertainty is any outflows that reach the terminals. At this time, that potential looks low, with a favor towards and easterly or southeasterly outflow, but there is currently only a ~10% chance of 35+ kt winds gusts. Skies will remain BKN through the overnight and into tomorrow due to the active weather this evening, with improving sky conditions going into tomorrow night. Southeast California/Southwest Arizona including KIPL and KBLH: Southeast winds will be favored at KIPL and south/southwest winds at KBLH through the period. The threat for thunderstorms looks again to be confined to higher terrain areas tomorrow, thus there could be another low potential (10-30%) for outflows to reach both terminals tomorrow afternoon. Otherwise, skies will remain FEW- SCT, aside from showers/storms that migrate off the higher terrain that cause occasional BKN high clouds. && .FIRE WEATHER... Monsoonal moisture will continue to remain in place during the next several days to result in daily thunderstorm activity, especially during the afternoon/evening hours. Activity through the first half of the week will be confined mainly across the AZ high terrain, with chances for activity for the lower deserts increasing by the latter half of the week into next weekend. The biggest thunderstorm hazard will continue to remain outflow winds, which will result in sudden directional shifts and strong gusts, exacerbating issues on any ongoing wildfires and new starts. Otherwise, the general winds will continue to follow diurnal tendencies with occasional afternoon upslope gustiness of 20-25 mph. MinRHs today will range between 20-30% area wide and fall slightly into the 15-25% range by the middle of the week with good overnight recoveries. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Lojero AVIATION...Young FIRE WEATHER...Lojero